Retrograde menstruation happens when tissue that lines the inside of your uterus flows out in the wrong direction during the period—through the fallopian tubes. While this process can occur in many healthy women as well, women with endometriosis experience it differently. The out-of-place tissue can attach and start growing on surfaces and organs in the pelvic region. This can cause pain and inflammation.
Other possible theories on what causes endometriosis include:
- The immune system not destroying endometrial cells outside of the uterus the way it should
- Normal cells in the pelvic area changing into endometrial cells. This is called coelomic metaplasia
- Endometrial cells forming outside of the uterus before birth, so that during puberty, those cells form endometrial lesions
- Endometrial cells may be transported through the blood or lymphatic vessels to another location
to learn about the inner workings of endometriosis and why it hurts.
What puts a woman at risk of endometriosis?
Scientists aren't sure, but some possible endometriosis risk factors include:
- A family history of endometriosis
- Never giving birth
- Starting your period at an early age (before 11 years old)
- Short menstrual cycles (fewer than 27 days)
- Long or heavy periods (What's a "normal" period? Find out here!)
No one demographic or ethnicity has been labeled as a risk factor for endometriosis.
References: 1. Burney RO, Giudice LC. Pathogenesis and pathophysiology of endometriosis. Fertil Steril. 2012;98(3):511-519. 2. American College of Obstetricians and Gynecologists. Practice bulletin no. 114: management of endometriosis. Obstet Gynecol. 2010;116(1):223-236. 3. Fischer JR. APGO Educational Series on Women’s Health Issues. Diagnosis & management of endometriosis: pathophysiology to practice. Association of Professors of Gynecology and Obstetrics; 2012. 4. US Department of Health and Human Services. Endometriosis. http://www.womenshealth.gov/a-z-topics/endometriosis. Updated April 1, 2019. Accessed January 8, 2020. 5. Mayo Foundation for Medical Education and Research. Patient Care & Health Information. Diseases & Conditions. Endometriosis. https://www.mayoclinic.org/diseases-conditions/endometriosis/symptoms-causes/syc-20354656. Accessed January 16, 2020.